Antibodies against gamete surface components are effective probes for the analysis of gamete interactions in fertilization. Fertilization is arguably the most biologically important event in life and can serve as a model for the study of cell interactions in general. Understanding of the mechanisms for cell recognition in fertilization would lead to the development of safe, simple and effective methods of fertility control. The proposed project will use immunological probes for specific gamete interactions and antigens in the annelid Chaetopterus because this species has features in its fertilization which makes it an attractive model system for the studies. Specific antibodies will be isolated by immunoblotting and by immunization with purified antigenic macromolecules. These will be used both as probes to determine which components of the sperm and egg vitelline layer interact in fertilization and to map the domains of the antigens on sperm and eggs by immunofluorescence and immunogold labeling techniques. This would ultimately lead to a molecular description of the components involved in fertilization and their mode of interaction.